1. Field of the Invention
This invention relates to the field of archery.
More particularly, the present invention relates to an item of archery equipment generally referred to as a compound bow.
In a further and more specific aspect, the present invention concerns improvements to materially reduce the effects of induced torsion in a compound bow limb.
2. Description of the Prior Art
Archery, the art of shooting with bows and arrows, is an anchient practice which has been continued to the present time. The traditional bow was merely a strip of flexible wood having a string or cord extending between the tips. Evolution over the centuries has resulted in the compound bow, familiar to modern archers.
Originally, archery equipment was exceedingly simple 2nd highly ineffective. The bow limbs, the portions of the bow extending in either direction from the handle section to the respective tips, were not torsionally balanced. Accordingly, in a condition referred to as "system torque", the tips of the bow pulled unequally upon the string, imparting erratic flight to the arrow.
Another pronounced problem with early equipment was the phenomenon known as "archers' paradox" which concerned the attempt of the arrow to have both ends travel in the same straight line to the target. The problem arose as a result of the rear tip of the arrow being propelled directly toward the target by the string which moves in a plane bisecting the center line of the bow and perpendicular to the target. The forward tip of the arrow, however, extends laterally from the plane of the string as a result of the width of the bow around which the arrow must pass.
Over the years, bows remained relatively unchanged. With the advent of modern materials and laminating technology, bow limbs were greatly improved. The new laminated structures, usually wood between layers of fiberglass, were of improved strength and balance. Grip sections incorporating relatively shallow "sight windows" also appeared. "Archers' paradox", though not eliminated, was reduced and made more reliably predictable.
In very recent times, there emerged the present-day "compound bow" consisting of extremely stout bow limbs secured to a central section or "handle riser". Generally fabricated of metal, the central section was of sufficient strength to accommodate a "sight window" of ample depth to eliminate the anchient "archers' paradox". A system of string, now more appropriately called cable, extending over pulleys at the ends of bow limbs allowed the average archer to draw a bow approximately twice as powerful as had previously been the case.
While providing numerous advantages and correcting various previous problems, the compound bow did not represent perfection. Especially notable was the twist or torsion introduced into the bow limbs as a result of the unbalanced loading of the pulleys. Characterized as "limb/pulley torque", it has remained a major cause of inferior arrow flight.
Typically, the compound bow limb is of comparatively uniform width terminating with a relatively broad tip which is bifurcated to form a pair of tip sections. A two-groove pulley and a single-groove roller are carried upon an axle extending between each of the tip sections. The roller, usually substantially smaller than the pulley, functions as a "tieoff buss". Three segments of a single cable extend between the tips of the bow.
A first segment of the cable extends between outboard grooves of the pulley. The other two segments extend between the inboard groove of the pulley and the roller at the opposite tip. Termed the "bow string", the first section is generally parallel to and spaced from the longitudinal axis of the bow. The other two sections are oblique to the longitudinal axis, crossing at the approximate midpoint of the bow. The ends of the latter two segments are terminated or tied off at the roller.
A primary recommendation of the compound bow is the mechanical advantage provided by the arrangement of cables and pulleys. The force with which the archer is required to hold when the bow is fully drawn is substantially less than the force by which the arrow is propelled. The advantage to the archer is further enhanced by the use of eccentric or off-center mounted pulleys. A usual arrangement provides approximately a 2:1 mechanical advantage.
There are, however, counteracting disadvantages. As the bow is drawn, the force on the bow string is approximately one-half the force on the other strings or cable segments. A force of corresponding magnitude is applied to each of the corresponding pulley grooves. In a bow capable of propelling an arrow with sixty pounds thrust, for example, thirty pounds of pressure is applied to the outboard groove of each of the eccentric pulleys. Correspondingly, sixty pounds of pressure is applied to the roller or "tieoff buss" and to each of the inboard grooves of each of the eccentric pulleys.
The placement of the pulley is rather rigidly defined. Ample strength must be maintained in the long tip sections to support the load transmitted through the pulleys to the axles and ultimately to the tip sections. It has been conventional procedure since the advent of the compound bow to align the pulleys in juxtaposition on the longitudinal axis of the limb between tip sections of substantially equal proportions. The forces absorbed by the limb, however, are asymmetrical or unbalanced relative to the longitudinal axis of the bow.
Consider, for purposes of illustration, a system in which the inboard groove of the eccentric pulley is in approximate alignment with the longitudinal axis of the bow limb. The outboard groove of the eccentric pulley and the groove of the smaller roller are substantially equally spaced on opposite sides thereof. Accordingly, unequal force is applied to the tip sections of the bow limb.
As the bow is drawn the tips move rearwardly, deflecting the limbs along the plane of movement of the bow string. Concurrently, the tip sections supporting the greater force move laterally, introducing twist or torsion into the bow limbs. Both movements store energy within the bow limbs.
Upon release of the bow string, the energy previously stored in the bow limbs is unleashed as the limbs straighten and return to normal or unstressed configuration. The energy, transmitted through the bow string, is the propelling force for the arrow. In the conventional compound bow, the propelling force includes a linear component directed toward the target as a result of the rearward deflection of the limbs and a torque component as a result of the twisting motion of the tips. The speed and direction of the arrow is the resultant of the components of the force.
It is well recognized by those skilled in the art that the arrow is whipped sideways, and therefore inaccurately, in response to the torque. It can be demonstrated that one-eighth of one inch, a realistic measurement depending upon the weight of the arrow, of twist of the pulleys can result in as much as ten inches of lateral dispersion of the arrow at forty yards.
Limb/pulley torque is responsible for additional undesirable results. Frequent longitudinal twisting accelerates fatigue and breakage of bow limbs. Also, the cable can slip from the grooves of the pulley which is tilted, thereby unstringing the bow. Further, arrow efficiency during downrange flight is adversly affected, reducing speed and penetration.
The prior art has proposed various solutions to the foregoing problems, including altered arrow design and various attachments and paraphernalia for bows. None of the suggested remedies has provided a satisfactory resolution. It would be highly advantageous, therefore, to remedy the foregoing and other inherent problems in the prior art.
Accordingly, it is an object of the present invention to provide improvements in archery equipment.
Another object of the invention is the provision of an improved compound bow.
And another object of the invention is to provide an improved bow limb of the type used in connection with compound bows.
Still another object of this invention is the provision of means which materially reduce the effects of limb/pulley torque.
Yet another object of the immediate invention is to provide means whereby the resultant propelling force of the bow string is substantially directed toward the target or point of aim.
Still another object of the invention is the provision of means to eliminate twist in a bow limb.
A further object of the instant invention is to provide a balanced bow/limb system.
And a further object of the invention is the provision of an inherently balanced system without requiring attachments or encumbrances.
Still a further object of this invention is to provide an improved bow limb which is less susceptible to fatiguing and breaking.
And still a further object of the instant invention is the provision of improvements of the foregoing character which are relatively simple and inexpensive to effect.